What is with this guy?

I am currently with my partner of 2 years and I live with him.
Just for the record I am not used to getting attention from any guys and when I was at school I was not seen as very pretty to the boys. They would pick on me for my looks and the girls would pick on me for being quiet, being “keen” and not having many friends.

For the past 3 years I have been at my current company I have been receiving attention from a guy who I have been told is 3 years older than me and is a senior manager. I used to work under him for 18 months before his department gave me up to another team. I have not in any way encouraged him. I smile at him, but I smile at anyone who I am friendly with. This guy is a social drinker, has very opinionated views on anything LGBT and transgender - he does frown upon it and has expressed contempt about this sort of thing and he swears a lot. My friends have told me he has lived on his own since moving out of his mum's 2 years ago and he is not seeing anyone, but I didn't even ask if he does live on his own or sees anyone. These same friends are friends with my parents and know that I am spoken for.

The first time I became aware of something was when he took me off for a chat, sat down first and then when I sat down after he did, he shifted really close to me, enough for the sides of our bodies to touch and for our feet and legs to press and rub against each other. He is a big guy but there was room for him to move and looking back I think to myself he could’ve moved if it was accidental, but he didn’t move away at all.

The way he was sitting and leaning in towards me had brought part of the front of his body behind me and his arm was pressing into my back and I noticed people walking past us and looking over at us which made me feel uncomfortable.

I didn’t know how to react at the time, I felt almost frozen to the spot and didn’t know what to say. He told me I am a good worker and told me not to leave the company and this chat must have gone on for a good 20 minutes before we went back to work. A few months later he said something suggesting to me to sleep with him at a hotel if we happened to be on holiday in the same place together.

He told me once when I was alone with him (everyone else had gone home) that he found my social media page and that he saw and liked my photos before sending me a message asking me for my mobile number. Because he is senior in the business I figured he might have asked me in case of emergency. But thinking about it further, he was simply my client and not my actual employer (I worked for an agency), he could’ve asked me right then for my number if it was for work and also not my direct manager but a manager regardless.

I told him I did not read the message he sent because I didn’t have access to my social media account – which was true because I couldn’t remember the password and I didn’t use it that often. He seemed frustrated about what I said. He also knows I am with someone.

A month after I left his team I encountered him again and he asked me who I was working with and who was my manager and so on. He then told me once that job came to an end to not leave the company and said if I needed any help with anything to let him know.

I encountered him a lot more the following year (last year) because he started working closer to where I was and I noticed other things happening. I caught him looking down the front of my tops, looking at my butt and legs when I wear trousers/leggings/jeans and up my skirts and dresses and I always dress appropriately for work (though now we are in lockdown and we are all working from home)

When I have caught him at it, he just looks straight at me and grins widely. If I bump into him and he is with someone else he looks down at my body and then up into my eyes and I can’t even give him a lot of eye contact because he looks so intently at me all the time. All I can do is give him 1 or 2 seconds of eye contact before I look away or look down at the floor.

He doesn’t like other people speaking to me by the looks of things, either, because I have caught him standing close by and watching the whole time I am there, almost glaring at me or the person I am speaking to. A friend of mine he works with says that this guy commented on me when I was at a previous party but wouldn’t go into any detail what he said, because that to me meant that he was being rude.

He once insinuated that my partner isn’t treating me right and has told others that my partner isn’t looking after me properly. Now my partner buys me flowers, does things around the house for me when I am not well or have had a bad day, he buys me drinks and meals and he suggests we go out to places and do things (not sexual) together. I mean, if this guy thinks he can do any better I would like to know how he plans to do that?

He has watched me leave work and use the company bus to go home (when he has walked out of the building or when he is in his car) he even makes a point of going over to the bus and looking through the windows, he has tried to approach me on my own during my breaks and also has been asking other people I used to work with for my name, my manager’s name, where I work in the building, if I am leaving…

I mean, I like him as a friend because he was always nice to me, approachable, caring and honest. And not afraid to speak his mind, but I really don’t know how best to approach this or if it’s worth saying anything at work to anyone, because I have a feeling that one of my friends at work is telling him when I am thinking of leaving because they are active at the same time I say this and soon after I say this, the guy goes on his own page and posts sad and really negative stuff suggesting he isn’t happy. This other friend has told me not to leave and give myself more time to “feel right” about leaving or staying.

Everyone I have spoken to (employment related) says what he is doing is wrong and I ought to report him - but he would know straight away it was me who was responsible and I don't want to make him angry or have him hate me. I have no experience with guys flirting with me and I got with my current partner because we met up, had same interests and views and we bonded without the need to flirt with each other.

Any advice appreciated.