Have you not read Jesus’ warning? Matthew 10:34–36 Do not think that I came to bring peace on the earth; I did not come to bring peace, but a sword. For I came to set a man against his father, and a daughter against her mother, and a daughter-in-law against her mother-in-law; and a man’s enemies will be the members of his household.
Consider Jesus’ ministry and the ministry of the prophets before Him as recorded in the Old Testament. They were sent to God’s people and were rejected, and nearly all of them were killed. When Jesus commands us to love our enemies, He especially meant those who are closest to us.
What you are running into and being frustrated by is called a ‘performance orientation’ or ‘performance-oriented religion’. Many Christians still try to live up to the standard of the Law after they’re saved as a Christian duty. This holds even for those who understand that they needed Jesus as savior because of their inability to live up to the requirements of the Law. The book of Galatians was written to address this problem in the church. Most Christians who have a performance orientation problem don’t even realize it, and they are just trying their best to honor God the best way they know how.
Now with respect to your non-Christian boyfriend and the concerns you expressed. The Bible says very clearly that Christians should not be unequally yoked together with non-believers. Like the rest of the commands found in the Bible, God tells us these things for our protection from harm and for our blessing and well-being.
Why dating or marrying a non-believer is harmful (besides the fact that it is disobedience) is that the people who are closest to you are going to exert a strong influence on your spirit and soul. If that influence is from a godly person, then it will help draw you closer toward God. If it is an ungodly influence, it is going to tug at you in the opposite direction.
Based on what you wrote, it sounds like this is already starting to happen. One or more of your Christian friends/acquaintances said something to you about dating a non-Christian which you didn’t like hearing. This appears to have caused you to start looking more closely at your Christian brothers and sisters around you and taking greater note of the failings and shortcomings. This in turn is causing you to distance yourself further from other Christians and to start questioning whether you want to continue in fellowship with the Church.
I don’t doubt you when you say that you love God, but what is certain is that after having soul-tied yourself to your boyfriend you won’t love God as much in a year from now as you do today. Not because you’re bad or evil, but simply because of how the spiritual dynamics work and the influences you’re choosing to surround yourself with.
At the end of the day it is your life to live and your choices to make in how you want to live it. God explained to the Israelites that the choice they had to make was to choose life by obeying Him or choosing death by not doing so (Deut. 30:19). We each get to make the same choice. You may be a sinner saved by grace, but there are two conditions on the promise that all things work together for good: you have to love God AND be called according to His purpose. (Disobeying does not constitute following His purpose for you.)