Is it normal for a man to constantly joke about anal sex with one male

Well, I don't know whether I am being paranoid but I think one of my husbands new male work friends is trying to crack onto him. His friend has a girlfriend which he is always putting down to my husband and his friend texts him every night after work, weekends and even when we went away on holiday. I am OK with all the texts ( I do find them a bit full on) but the messages he writes majority of the time turn sexual. His friend constantly makes jokes about my husband wanting it up the ass and loving bum sex. Although when i have had a look at my husbands texts he hasn't recipricated he hasn't said get lost either. I spoke to my husband and he defiantley says his friend is just that and says that is how all guys act. I want to beleive him but double the texts with the constant texting after work, weekends and the bad mouthing of his girlfriend I am concerned he is testing the water with my husband to see if he gives him something back. I am all for banter and taking the josh out of things but could his friend be bi?