It is not a huge surprise to find that for some people receiving acts of service is how they feel loved. Even if it's not your primary language, who doesn't like it when your spouse picks up their laundry off the floor, and takes out the trash? Even I appreciate it, and acts of service is not my language at all! Can you imagine how it feels to have the feeling that you do everything for everyone in the house, partly at least because you are trying to tell your family that you love them, while no one seems to love you in return?! Really sad situation!
How can you tell that you sweetheart is an acts of service type? well...when they are honoring their friends and family, how do they do it? Do they host a big party? Are they the first one to jump in if someone is needing help because of sickness or injury or a new baby? Then they just might be the serving type. I find this one can feel hard to adapt to, because if you are not a serving type, it can be hard to do the acts of service and really get that this is an act of love. But with some determination, and reminding yourself why you are doing this stuff, you will find that the payoff happens pretty quickly, helping you to remember that this is the best way to love your spouse.
In general, to find out the love language of your spouse my first advice is to buy the book, read it together, and then take the quiz in the back of the book. Use that to help you each find your language, and then tell eac0h other what it is! If you happen to be in a marriage where your spouse is a closed type and not into reading marriage growth books, then it's a bit more difficult. You can read the book yourself and take the quiz from your knowledge of your spouse. In the end, if you just take some time to observe closely how they are with friends and family, and you too (sometimes couples withhold the main loving language they speak from their spouse because they don't feel loved by them - this makes it hard to figure out by watching how they are with you), then you can determine their love language, and then love them in that language!