altruism or being used?

You were very compassionate in how you reached out to that person. Mine too was a very similar story. I have no ill will in any way what so ever against that person, but I now keep my distance with him. What I would like to tell you here is that you have to learn compassion for the people around you, and also compassion for yourself. And most importantly you need a good sense of humor.

It is the ability to laugh at the foibles of human nature that leads both you and the person that you reached out to, to doing what is unskillful. We have to learn to laugh at that kind of behavior, but it’s a good-natured laugh. It’s not nasty or mean. It’s the recognition that we all have had those impulses, and we can see the foolishness in giving in to them. The virtue of humor is that it allows you to step back and separate yourself from what you’re laughing at. If you can develop a sense of distance between self and the act, then you can laugh at human behavior. So when you can laugh at yourself, you’re putting yourself apart, separate from your foibles and above them. Then you will learn from any unskillful actions or thoughts from your part, and learn to keep on giving, and reaching out to others without any form of expectations in return.

In Buddhism, there are two kinds of friendship: (i) ordinary friendship; & (ii) spiritual friendship.

In ordinary friendship, Buddhist principles ensure what is called 'false friends' or 'false friendship' does not harm us, including economically. The principles of 'true friendship' & 'false friendship' are listed in this link in the 2nd section, which begins with: "These four, young householder, should be understood as foes in the guise of friends...". You may read this thoroughly & thoughtfully to help provide perspective &/or guidance.

In what you described in your post, the impression of 'false friendship' does not appear to exist because: (i) you have volunteered to help him; (ii) you are not threatened economically; and (iii) you are not being taken advantage of sexually or illegally.

Therefore, your situation appears to be an issue of spiritual friendship. In Buddhism, spiritual friendship (metta-karuna) or 'altruism' is unconditional; it is not given to receive anything in return; it is selfless.

From a Buddhist perspective, since it appears you are not being threatened or harmed, your issues are those related to hurt from 'pride' or 'conceit'. This kind of 'egoism' the Buddhist path seeks to end or overcome because it causes suffering. A mind training verse is as follows:

When someone whom I have helped, Or in whom I have placed great hopes, Mistreats me in extremely hurtful ways, May I regard him still as my precious teacher.

Eight Verses for Training the Mind

Buddhism would recommend to continue helping your friend in a selfless manner & identify the problem as your 'pride' or 'ego' rather than your relationship being something inherently dangerous you must urgently end.

While his new girlfriend may not be ideal, ordinary people do often get possessive in relationship so you can give them some space rather than officially break your platonic friendship.

Ultimately, it is ideal the new girlfriend trust you and express gratitude towards you given you have helped her new boyfriend in an extraordinary & praiseworthy way. Give it time. His new love affair may not work out, anyway (since she sounds very possessive & controlling), thus he made need your help & support again when it falls to pieces.

In summary, true spiritual friendship & altruism cannot hurt or harm us. As long as the five Buddhist precepts are not transgressed (namely, physical violence, economic theft, sexual exploitation, deliberate lying & drug addiction/enabling) then we cannot be harmed or hurt; unless we ourselves are controlling & possessive, in which only our own pride & attachment hurts us.

My answer: keep a low profile! (but be prepared for when he needs you again).

In Buddhism, this is called 'upeka' ('equanimity'), which literally means: 'to watch over/observe a person in a detached manner until we have the opportunity to help'. An intrinsic element of 'upeka' is giving others the space to take responsibility for & learn from their own karma (actions).

Since you have genuinely helped him, you should be satisfied in your own virtue & goodness. One meditation in Buddhism is reflecting upon your own good altruistic deeds (cāgānussati).