Stuck! In love whilst getting married

Ok so I won't bore you with the full details. But basically, I've been with my fiancé for 10 years. It never was lust with me, I ended up giving him a chance after 6 months of chasing me. Then 10 years later we have 2 gorgeous sons together. We're due to get married next April. However, I have a confession. I'm in love with someone else. He's perfect in my eyes and I just melt everytime I'm with him. I've been sneaking around spending time with him nearly a year now. I cannot marry my fiancé as I'm not in love with him. But he is head over heels for me. I wanted marriage etc 5 years ago. It feels too little too late for him. He's taken me for granted and now he's realised but I feel it's too late. I just need unbiased advice. Any gaps you want me to fill in, I will do. But everything else with this other guy is amazing, he makes me laugh, has made me love myself again, tells me how beautiful I am constantly. All the things much partner should have said but didn't. Any help is appreciated. Thanks ks

*As for your fiance: You already know the answer. You said it yourself: "I cannot marry my fiance as I'm not in love with him". You are being unfair to him by pretending to be faithful while sneaking around hanging out with someone else. Now is the time for moral courage. Tell him the truth as soon as possible, apologize to him, give back the ring, and get yourself and your kiddos some support (family, friends, professional) to deal with any emotional fall-out. It may seem very hard, but it's going to be OK. Hugs to you. *As for this other guy: You seem to be using him as a "life raft" and for self-validation. You may get the super "butterflies in the stomach" when you are with him, but you do not seem ready for a healthy relationship (with anyone) until you can make *yourself* laugh, soothe-yourself, and know how beautiful you are without needing anyone to romance you or chase you down to reassure you of it. *Conclusion: Your relationship history hints that you sacrifice your own integrity and inner voice of truth to gain validation from others: once when you went against your gut feeling and gave your now-fiance "a chance", again when you got engaged to him, and again when you got involved with this second guy despite having a commitment to the first. Work on and commit to your goals, your health, and your well-being (i.e. learn how to self-validate and self-soothe) before making commitments to anyone else. If you don't-- you will be selling yourself short, and hurting others' feelings in the process.