Sounds like you want the best of all worlds, or maybe you’re not ready for a commitment type of relationship, which marriage is. You obviously have sexual needs that he can’t satisfy so you’ve met your needs elsewhere. Is he aware of this? How do you think he’d react if he knew? If he finds out would he dump you? It might still be an issue after you got married. Sometimes people can have many relationships that satisfy various needs. He seems to speak to you as a person/friend etc. The other lover is more physical. Point is unless you reconcile the fact that one set of needs won’t be met with him, or might be if you try, then it’s better to go along as you are doing. Until there is pressure on his part to get married there’s not necessarily a reason to address it unless you want to. Also, know that anytime you choose an action (like sex with another person), unless the rules have been previously established (and even then there’s no guarantee), the other person involved (in this case the 2 year relationship) will somehow be affected. You are the only one familiar with all the people involved so you should be aware of what gains and losses could be possible.