Boyfriend cheated on me because i am in hospital?

I've a bad health condition at the moment although recovery should happen within a year.

In the beginning my boyfriend was so supportive and then after me being in hospital for 6 months I found out he was talking to and hanging out with another girl.

My boyfriend has mental health issues where he can't handle too much stress. He was abused often as a child and was put in foster because of this. When I first met him years ago, I thought he was gay but he's just that way because of his childhood and upbringing so he's very sensitive and almost womanly.

I feel like that's why he needed someone. He has friends but they're all busy with their partners.. so I think he needed support. Now I don't know what to do I am still in hospital but saw a few photos of them on a friends page and I almost broke in half.

I love him to pieces and he's always bent over backwards to support me but now this. She actually looks like a man is twice his size and wears men's clothes she's in a photo of a party I was supposed to go to with him...his sister's 21st birthday and they're close..

I don't know what to do... is this Normal? I feel like it is a normal reaction to being emotional and needing support I used to be his rock...i always felt like the one who wore the pants but because of me being sick I can't do that...

I can't accuse him I don't even know what they are.