Is my friend in work interested in me?

Bit of context, we both work in a call centre and both guys same age range. We’ve worked together for 3 months but I ended up quitting. Before I quit we never spoke a single word despite being in the same team. But I then returned to the job and we started speaking to the point where he talks to me more than anyone else and we go on breaks together in his car.

He is an introvert and never spoke to anyone else in the office, and everyone keeps saying how surprised they are that we don’t stop talking during our shifts. I do like him a lot and spending time with him is so much fun. We spend time outside of work and get a drink every Fridays.

He has told everyone in the past he’s straight, but there are some signs which confuses me. When we’re starting to get attention in the office and our other colleagues comment on us, he’ll start to back off for a couple of days but we still spend break together. Also, if we’re not sitting together we’re constantly messaging each other. We walk out of the office together most nights.

The biggest parts which confuse me is whenever I go out with my friends he’ll text me and even ask who I’m out with. Plus he always ask me questions like he’s trying to get to know me, and if I’m spending time with other people he’ll either listen to our conversation or try to get my attention.

Just a bit confused and wanted second opinions, if he is closeted I didn’t want to put any pressure. At the same time, if he is straight and not interested didn’t want to ruin things.