There comes a time when you've got to stop being a pushover and start taking control of the situation. When people back up into a corner, they explode with emotion; that isn't healthy. Clear and direct communication is how things should be handled, even forming contractual agreements and enforcing the agreements laid out in the terms can also serve as a benefit.
People are selfish, and that's ok, but if you're not defending yourself, who will? Your mum? Possibly. There are many times when people will take advantage of you; they will take advantage of your kindness, wealth, generosity, and time. There is nothing more precious than time, so take the time to prioritize yourself above other people once in a while. Selflessness and selfishness are both double-edged swords. If you're too selfless, you give to everyone but cannot provide for yourself. If you're too selfish, you take advantage and try to exploit other people only for your benefit. There needs to be a balance between the two where you're not being too generous and not being a complete pushover.
If you feel you are being too kind, you've got to snap out of it and have a little more pride. Know your worth. If someone is taking advantage of you and you aren't defending yourself, then at the very least, find avenues to progress or gain from that interaction. You don't HAVE to be confrontational, but you must take a stand.