I have a female friend I've known for about 3 years who I actually dated for awhile back when we originally met. Some major things happened in my life which caused that relationship to halt after only a pretty short time, like 2 months, but we remained in touch and then have reconnected some just over the last six months. We're both in relationships now, but through talking, it has come out on both sides that neither of us are thrilled about our respective relationships, and we both view each other as a potential long term partner, like with marriage and kids etc. We have agreed to go on platonic dates (lift weights together, have coffee and talk, etc) and see how they go with the implied understanding that if they go well, maybe we should form an actual romantic relationship and be together.
My question is, how ethical is this? We're technically not cheating because we're not being intimate, and both of us aren't very happy with the idea of marrying our current partners, but at the same time, obviously our partners would not be happy if they knew our true intentions. However, everyone is just trying to maximize their own happiness in life... What is best here?