I've been happily in a relationship since I was 15 (21 this year). However, I have no friends (okay, maybe 1, who I see once a month). Sometimes, when other guys talk to me (outside of work/school project settings), I have difficulty trying to tell if they are genuinely being friendly or whether they are only being friendly now and having the intention to try their luck later. This makes me very anxious as I don't want any jealousy to come up in my relationship when I show my bf such texts, and I become stuck in a dilemma of whether I should continue being friendly with the guy and continue chatting (and hoping to make friends) or end the interaction. My bf told me that talking to guys who are just being friendly is okay, but I really have trouble telling the difference between genuine friendliness or "chatting with you now and planning to ask you out later". I also become hyper-conscious about whether I come across as flirting. Does anyone else get anxious when talking to other guys because of this too?

For example,

Case 1: Just today, I was on a local online used marketplace and a guy about my age bought a food deliveryman shirt from me. He walked over to the apartment where I live since he stayed relatively near. Afterwards, he texted to thank me and told me that the shirt was meant for a prank for his friend's birthday in a very friendly way which he wasn't using before I met him irl. I asked him what prank it was and thanked him for the deal. He explained his prank to me, and I replied that that was quite sweet and that I hope it works out, very subtly trying to put an end to the interaction. Then he laughed and asked me why I had the shirt. Because such conversations don't usually happen after deals, I'm in a dilemma whether to reply him because part of me is scared that he may have intentions to eventually ask me out. But part of me also wants to think that he may just be friendly.

Case 2: I've also talked to guys in the past to whom I've explicitly mentioned my bf and they never asked me out, and one of them even suggested going to McDonald's with me and my bf.

Case 3: I've also talked to a guy (a teammate on my sports team) who knew I was taken. He was being very friendly with me in my DMs by giving me sports advice but eventually suggested we went out and practiced our sport together. When I asked him whether we could bring along more teammates, he said it was too troublesome because everyone else lived further away from the sports centre. Down the line somewhere, I asked my bf whether he was comfortable with me going out to practice the sport alone with the guy and he said he wasn't, so I told the guy exactly that. The interactions ended shortly after.

It's not that I think every man who talks to me have interest in me, but I honestly cannot tell the difference between genuine friendliness and "friendliness to warm me up and try their luck later". It's just all very confusing and gives me anxiety. What do you men and ladies think of these 3 examples above (what were their intentions?) and does anyone have any advice for navigating such interactions?