Need help with Tennant

[Brian Corbett]

Hello Bigger Pockets community

I have a 2 year tenant who has a girlfriend living in the house (single family) who isn't on the lease. This is a breach of our agreement however the tenant isn't breaking any other lease terms otherwise. I have attempted send him a letter about this but it was returned. I think I know I need to deal with this but on the other hand I am somewhat reluctant to do so. I need some encouragement. The tenant is kind of a grouch and I just don't feel like dealing with him, especially since he pays on time and his rent is slightly over market.