Am I doing something wrong?

So long story short me and my bf have been together for a little over a year now. things are always great when we’re together and we’ve never had many major issues up until now, all of a sudden he’s super busy and can barely text me other than to let me know he’s going to bed. I know he doesn’t have a great home life and his mum asks a lot of him but he never used to be like this he used to find the time to message me and to remind me he loves me or things like that. he knows things are rough with my mental health right now for personal reasons which he’s aware of. Now I could be overthinking and overreacting but he’s suddenly gotten close with this girl again we’ll call her Mary, well all through last summer they were talking and I’ve never really been the person to stop him from being friends with anyone and as she’s a mutual friend of mine I didn’t think anything of it so this carried on for a few months. ever since then he’s been lying to me about where he is and what he’s doing. He goes to his mates a lot recently which is fine I’m glad he’s seeing his friends but he always tells me he’s going to his dads and Mary tells me where he is and as I said previously he barley answers my messages. So I’m confused, I know I’m not the easiest to be with because of my issues but I try my hardest to be normal despite this but he just doesn’t seem to care anymore and I don’t know what I can do to improve this. tbh it’s making me feel like crap and that maybe he just doesn’t feel that way about me anymore or wants something new. I should also say I’m the only girl he’s ever been in a relationship with. Is it something I’m doing? I’ve asked him before and he’s told me I have nothing to worry about with Mary and every time I bring up the fact he lies to me about where he is he just apologises and says he’ll stop but sometimes he just doesn’t have the time or is busy and I’m just wondering if he’s that busy to message his friends and Mary then why can’t he message me. It’s getting to a point where I’m starting to hide away and I don’t know if I should trust him as much because of of him being secretive and him just not seeming to care. I just don’t know what to do right now.