Eeeehhhhhh

Based on what I have read, I think an actual conversation (heart to heart) is more necessary than a jealousy arc. Of course that'll only be the last solution because DRAMA, but MC accepting being around a super flirtatious dude just to make his lover jealous only proves the point. It'll look like the MC is truly interested in exploring relationship options, and in an extreme scenario may even be let go by his lover. Lowkey, they may even have a small separation or break up bc one wants to prove a point (which could be better expressed if he reaffirms his stance that 'although I do not have extensive relationship experience, I am a grown adult with confidence in this relationship and I want to be treated more as an equal despite our age gap because I want this relationship to work') and the other is losing confidence in their relationship (which could also be better expressed as "I fear that our relationship is unequal and that while I have had time to grow and develop, I do not want to stop you from doing so as well and I want to make sure that you are not wasting your time in a relationship that may not be the best possible one for you to have'). I say all this mostly cause I understand that some people may feel like their partner settled for them because their partner has had no other relationships for comparison, which can feel like one is holding the other back, especially in an age gap relationship where there is a natural lived experience and maturity gap.

Anywayyyyys, I wanna see them sit down and talk because I fear the jealousy arc will only further prove the lover's point and drive them apart because people aren't psychic. You can't know what you aren't told and if the MC is uncomfortable with the point and speaks about it rather than play games, there is a higher chance of his lover understanding why his words were painful as they showed a lack of trust and understanding about the feelings of the mc (as he is treated like a young naive person rather than as a proper grown adult with the ability to make his own choices about his relationship despite not having much experience). (●￣(ｴ)￣●)