Does his behavior sound suspicious/cheating?

My boyfriend of 5 years has a history of problems with pills. The other night I was on his phone and I found messages of him talking to another girl asking ber for Xanax and talking about smoking pot with her and her boyfriend. All the while he was telling me he was done with pills and I had no idea. Now I have trust issues.

Now on Facebook I keep seeing him liking a certain girl’s things and commenting on them (not always pictures). He doesn’t ever comment on her selfies but he does like them. It’s like almost everything she posts/shares he likes, and she does the same with him. This has been going on for about 2 weeks.

The other night my boyfriend sent me pictures of his penis at like 5am. He NEVER does this, ever. He texted that he was hard from thinking about our sex. Then last night I was giving him a blowjob and he was literally falling asleep and kept getting soft. This has never happened before. I confronted him about the pictures to see if I was the only person he was sending pictures to and he said yes, he said he was looking at old pictures I sent him and it made him horny.

Am I just being paranoid? Do you think this is indicative of cheating?