Resentment is often the plight of people who tend to give a lot: a lot of time, emotional energy, empathy, thought, money...
As someone who identifies as generous with the giving of my resources to others I can speak first hand of the tendency to feel drained and resentful when I feel others aren't offering themselves to me in the same way when I'm in need.
Many of my clients identify the source of much of their distress as the unwillingness of others to help them despite the times in the past when they've offered them help (often, I've noted, when it wasn't even requested). Some people get a great deal of internal reward when they help others, but when its unrequited you can be presented with a conundrum. For some people helping others can over time leave them feeling taken advantage of, but not helping others leaves them feeling disconnected and anxious.
What begins as hurt can develop into resentment and left unchecked this can boil over into bitterness. So, what can be done to achieve balance and reduce that taken advantage of feeling...
Be boundaried with who you offer your resources to
You cannot give to everyone. More importantly you don't need to give to everyone. If you're inclined to give rather than take, then creating boundaries about who you do and don't give your resources to is an important part of protecting yourself. This doesn't mean protecting yourself from other people, but protecting yourself from...yourself! Identify who you think will appreciate you making the effort and focus on them. Think about who seems to not quite appreciate or acknowledge when you make an effort and respond to different people accordingly.
Adjust your responses depending on the different needs people have
It can be easy to assume that everyone's needs are the same as ours. In reality however people's need vary a lot. Different people need a different level and type of attention. Resentment can develop in the gap between what you feel you offer people and what you feel they offer you. You can't control what people do or how they respond to you (and as I'm sure you're aware, doing something for someone doesn't mean it's coming back to you!). You can however control what you offer, which can start to create more balance and less bad feeling.
If you can find a way to gently gauge what people might be able to offer you, you can become a bit more choosy about where you put your resources. This might sound a bit mean, but in fact it's just a matter of acknowledging that other people have different levels of need. If someone isn't likely to acknowledge or appreciate your attention then it's not a good idea to give it to them anyway!
I've found that generally speaking, those who offer a limited amount of their own resources, actually need a limited amount from other people. Equally people who need a lot of emotional contact will often be able to offer this themselves and will acknowledge and appreciate the effort made.
By all means give your resources, but be choosy with who you give them to.
Adapting your approach, mindset and level of contribution to different people is not selfish. It's a way of taking responsibility of your own energy. It's also vital to ensure you have enough of your own resources left over for yourself and for those who will appreciate and make use of it. If you treat yourself as if you have endless resources you will at some point find yourself feeling empty.
Acknowledge that people have different ways of giving
The way that people express themselves is very varied...some people need and need to give a lot emotional contact and attention. Others see giving their time (in whatever way) as the ultimate expression of care. Some people identify money or 'things' as the currency of care. Some will identify listening impartially as the biggest gift, whilst others see giving advice and opinion as most indicative of their willingness to help. Some see giving people space as the best way to help someone, whilst others identify maximum contact and attention as key.
In other words, people need different things and they often give others what they need. If you generally need space when you're going through a hard time, you're likely to give space to others...unfortunately if the person on the receiving end of this happens to need a lot of active empathy and emotional contact it might seem like the person giving space is disinterested.
Try to acknowledge that no one is obliged (or sometimes able) to give you what you give them. That doesn't mean they don't care. It means they are a different person to you and therefore have different ways of understanding relationships and the needs of others. Remind yourself that a lack of response doesn't always mean a lack of care. There's no right or wrong way to offer support, only the expectations we have of what people should and shouldn't do. This is often based on what we think we should and shouldn't do. Try to drop the should's and see what happens.