I don’t think taking a lover is selfish but doing it in a sneaky deceitful way and denying your husband the truth, is. Living with the consequences of our actions is how we grow up. If you’re not happy in your marriage leave it or sort it. Maybe ask your husband if he is lonely , wants a cuddle, or some kindness. I wouldn’t touch this married man with a barge pole what is there to respect ? His integrity? If you are craving love , start by loving yourself , and that means by being honest, truthful, and courageous, not telling lies and sneaking around trying not to be caught. No one who does that likes them self much IMHO. Im not talking about something I didn’t experience. I faced this exact dilemma in my first marriage, I left, divorced, and it was a huge struggle , but I met my second husband knowing exactly what I needed in terms of love and affection and feeling my honesty and courage.