Relationship/pregnancy

I’ve been with my boyfriend for a little over two years now and things between us have been really rocky. In December o went to a friends house for a birthday party and wound up drunk and slept with a friend. I feel awful about it and it’s not something I would’ve ever done if I hadn’t been drinking. I want to tell my boyfriend, especially now that things have been getting better but I just don’t know how to do it. Then today I check my eve app and realized my period is 19 days late. my boyfriend isn’t able to have children. I want to take a pregnancy test but at the same time I just can’t bring myself to do it. If I am pregnant, it wouldn’t be his. I would lose him and he is honestly the only reason I get up most days. We’ve had our bad days but the good has always weighed it out. I feel so stupid and awful about what I did. I just don’t have a clue as to what to do