"More like a brother/sister relationship"

Is there anyone out there who's been through/going through this scenario?? Any advice/guidance etc would be more than gratefully appreciated.
Bit of background for starters is that I met my partner via the internet nearly 2 years ago. We immediately clicked when we met face to face and about 3 months later he moved in with myself and my daughter. For the first 6-8 months, everything was fantastic then, sadly my dad passed away. My parents live at the other end of the country so for about 2 months of our relationship I was down with my mum. Life, when I came back, seemed to pick up as my partner found a job and we seemed to be getting on fine again. Then again tragically my partner's nan passed away in July, he was extremely close to her (his grandparents practically brought him up), he was totally devastated. The pair of us suffer from depression, my partner's being far more ingrained than mine. At the end of July my partner, who keeps everything bottled up, seemed extremely down, when I asked several times what the problem was he broke down and said that he felt really alone and that, in a nutshell, I wasnt paying him enough attention but that he still wanted to try and work things out. I was spending far too much time on the computer when I should have been spending my time with him. I agreed that I would only go on the computer at certain times but he also agreed that if he preferred me not to go on, he would speak up and tell me. Life continued on, Christmas and New Year came and went and then just 3 weeks ago, after sinking into another depression mood, he told me that he was leaving. When I pushed him to give me a reason, he first of all said that it was because he thought I was taking him for granted (which, in all honesty, I probably was - asking him to do little errands for me when I was perfectly capable of doing them myself), he said that he just felt that he wanted to be by himself. A week and a half after he moved out, I found out that he was seeing someone else but that they'd only been together for 3 or 4 days; a fact which I know is true, but that they'd been talking to one another for a couple of weeks before he left. The girl involved has some extremely bad issues going on in her personal life and my ex doesnt need that - the issues have also now involved me which I am extremely upset and frightened by. Myself and my ex-partner's best friend have voiced our concerns and he has, so far, listened to our advice and has had no contact with the other girl for probably a week now. When pushed, my ex-partner has told me that he doesnt love me like a girlfriend anymore, he feels our relationship has become more like brother and sister (in hindsight, thats probably why our sex life didnt happen very often). I am still, just over 3 weeks on, totally devastated by the whole thing. I love him completely and, even now, would have him back in a heartbeat. He texts or rings me most days and we've been out to the movies, for a drink and I've been round to his flat so we're still really good friends. His best friend told him that he thinks he's probably made the biggest mistake of his life by leaving me and my ex agreed but if his feelings arent there, what can I do? Is there anyone who has been in a similar situation? I'm trying the "put make-up on, do my hair nicely, act happy" routine but I'm not sure how long I can keep it going. I just want to ask him outright to come home x