Know Your Job
Before speaking it is very important to know precisely what you are responsible for. You ARE responsible for expressing your feelings, but you ARE NOT responsible for making sure that the other person understands you or agrees with you. That latter responsibility is their choice, their job. You are responsible for putting your cards on the table (and leaving them there). It is not your job to pick them up (if they are ignored) and shove them down the other person's throat.
The Magic Formula
If we can learn to express ourselves using a very simple pattern, we are likely to achieve much more in the long-term and avoid unnecessary conflict. The pattern (formula) is this:
When you did X, I just felt Y.
When you didn't do X, I just felt Y.
When you said X, I just felt Y.
When you didn't say X, I just felt Y.
e.g. When you spoke to me in that way I just felt you were being unfair. When you haven't told me you love me for 3 months I just feel neglected.
If you are able to express yourself in this way, several good things are happening.
1) You are asserting yourself, and that is good for your mental health. You are saying, "Hey, I am here in this relationship, and I am entitled to say how I feel."
2) You are asserting yourself in an non-aggressive way. You are not blaming the other person (You made me feel X) and looking for a fight. You are accepting responsibility for your feelings.
3) You are not being silent, and therefore you are avoiding the build-up (and potential later explosion) of anger. And by expressing yourself you are less likely to be depressed.
4) You are not making people change, but you are doing the only thing likely to bring about change, which is present consequences (and people only change when they have a reason to change). You are saying to your partner, "You live in cloud cuckoo land, and in cloud cuckoo land actions and words and inaction and silence don't have any consequences, and you think you can do or not do, say or not say whatever you want and it doesn't matter. I am gently letting you know that in the real world actions have consequences and that whenever you do X I just feel Y."
By not keeping silent you are telling your partner that you want an honest and open relationship with them, and that you are not going to keep quiet about how you feel about the situation.
Remember, it isn't your job to make them change, but you are responsible for communicating how you feel.