What you are wanting to enter into is called a Polyamorous Relationship, where you have multiple relationships of varying degrees with more than one person. Some people are happy with only having one partner, while some individuals, myself included, feel as though they need/want multiple partners to feel fulfilled.
Since you've made a commitment to just one person, and thankfully have been steadfast in that commitment, the correct thing to do is to discuss the boundaries of your current relationship before starting another one. This should be done when the relationship has good footing, e.g that there wasn't a recent argument/fight. When appropriate, sit your partner down and explain that you want to have a serious discussion. You can assuage their anxiety by reminding them that you love them (or whatever terms of endearment that you use). No one like hearing "We need to talk."
Then you inform them what you've told us:
- You enjoy intercourse with your current partner, so you're not
unhappy with them.
- You are curious and wish to explore your sexuality a bit.
- From the sounds of it, this may just be the one time soliciting a sex worker to get it out of your system. But if there are to be more times, that's something that you'll have to determine and communicate with your partner. The details are really between you two.
- You are extending the same freedoms to your partner.
- Remind them again that this isn't about them and what they do/don't bring to the table. That solely you are curious and want to branch out.
Now there are to likely reactions that your partner may show:
- Understanding and even agreement
or
- Abject horror and feelings of betrayal
If they are willing to open the relationship, then the next goal is to establish boundaries and communication tactics. If they are not willing, then the question becomes if staying monogamous will be a deal breaker for you (which sounds like it won't be but you are worried that you may fall to temptation and cheat). Either way, the next sections should help with your relationship(s) moving forward.
Boundaries
This is important to establish because crossing boundaries sows distrust in the relationship. Your partner may have an opinion on what they feel like you should or should not do in your other relationships. Some partners are okay with their SO having full-on relationships aside from them while others prefer that their partner has purely physical relations with others but the emotional aspects of relationships are off-limits to people outside the original couple. In other words, your partner may be okay with you having other girlfriends/boyfriends/enbyfriends OR your partner may prefer to be your main relationship but having some friends-with-benefits (FWB) on the side is okay.
One of my partners has asked it of me to wear protection when "sowing my wild oats" which I follow because it's just safe to. Another partner asked that I don't disclose any particulars of my other relationships because they didn't want to know. Now is the time to learn what your partner wants/needs.
If your partner isn't okay with opening up the relationship, this is the time to discuss what you need to stay confident in your relationship. You seem worried about breaking your commitment to your partner. You can ask for help and/or accountability from your partner. Describe any behaviors or situations that you find extra taxing (e.g. staying out of the red-light districts even though there's a really good Thai place near that neighborhood). Then your partner can help you stay true to your word. I can't begin to describe what you may need in this situation since I'm just a stranger to you and your partner.
Communication
This is the big kahuna in polyamory. All parties need to commit to open, constant, and honest communication or the relationships are doomed to fail. I recommend this for couples who aren't poly either. I've had great success with my girlfriend doing a "relationship check-in" where one of us just asks for a status update. This gives an individual the opportunity to speak their mind. My girlfriend and I would do it almost monthly at the beginning of our relationship but now we find ourselves doing it almost quarterly since we've found our groove. Honestly, this is good to do even if you won't dabble in polyamory. IMO couples need to talk more.
Not poly related but one thing I think I'm gleaning from your question is that you want to expand your horizons and try new things. That doesn't necessarily mean you need to go out and solicit a sex worker. There are activities that you and your partner could do together. Visiting an adult club, trying out BDSM, maybe, if you can find people for it, swinging, which is sexual activity with other couples. There are even clubs that cater to the above. The key thing here though is to communicate to your partner what you desire and establish boundaries that you both can agree to so that sex is more enjoyable for all parties involved.
Good luck!