A girlfriend that I haven't seen in 42 years calls me and wants to reconnect. I'm in a long term relationship. What should I do?

Tell her thanks, but you are in a long term relationship and you wish her all the best, but think it's better to leave things as they are now.

If you have to ask, your long term relationship isn't really that committed. Generally people who are devoted to one person and in a committed relationship wouldn't have any doubts about what to do if someone else calls up or propositions you with feelings for you that are not appropriate. So the fact that you don't know what to do means you need to reevaluate your feelings and your level of commitment to this first woman, otherwise you are disrespecting the relationship, and she doesn't deserve that. Honesty is the best policy. Always.

It may be OK ro reconnect as a friend but make sure the ex knows that you aren't available for a relationship. If she wants more then a friendship then you should refuse her request since it would be foolish for you to jeopardize your current status.