First time question asker here. 

I am in a committed relationship (man with man). Last night I was drunk at a bar and fooled around with another guy. Kissing, touching etc. 

He was rimming me for awhile. While he rimmed me, I felt something try to go into my anus- about half an inch before I pulled away. It felt hard like a finger, but it shocked me and I ended up just leaving the situation straight away saying I had to go. 

Now I am overly worried that he might have tried to be inserting his penis. I don’t think it was because I could feel any lube on my anus, and it didn’t feel like a penis trying to insert, just a finger. But like I said my anxiety is now going crazy. 

Can I ask:

If it was a finger trying to go into, what risk am I exposed too? 

Also, if he was trying to insert his penis, even if just half an inch for 3 seconds, am I at risk? I don’t know anything about his status etc and I don’t take prep. 

The exposure you describe was low risk at worst, perhaps no risk.  Deep kissing is very, very low risk for acquistion of gonorrhea, close to no risk.  There no appreciable risk from other kissing, touching etc.  As for your other activities,  there is virtually no risk for HIV or other STIs from receipt of rimming and if it was his finger that you felt, the risk would similarly be zero- there is no STI risk from receipt of masturbation.  In the unlikely circumstance that it was his penis (I really think you would have noticed the difference), given the brevity of the exposure, the fact that most people to not have STIs, and that most single exposures do not result in infection, I would have little concern that I had acquired an STI and probably not bother to test unless I needed the reassurance that a negative test can provide.  I certainly would have virtually no worries about HIV.  If you do choose to test, the most important STI to test for would be for gonorrhea or chlamydia, both of which could be tested for with an anal swab any time more than 3-5 days after your encounter.  

I hope that this perspective is helpful.  EWH

Like I said, I don’t think it was his penis. But I can’t stop worry. For argument sake, if it was his penis inserted half an inch for 3 seconds, this really wouldn’t be a significant hiv exposure event? I understand there are other stds risks to consider, but I’m wondering if I need to try and get pep?

One follow-up remaining.  EWH