I am also not an expert on it, but I think you ought to read up on it some. Even after the US withdrew from the JCPOA, Iran continued to comply with the terms of the agreement until at least Feb-May 2019 [0, 1, 2]. Keep in mind that this is long after the US announced in October 2017 that they would not re-certify [3] that Iran was complying with the agreement and in May 2018 when the US withdrew [4] from the agreement. In the October 2017 briefing, President Trump mentions that Iran "has committed multiple violations of the agreement. For example, on two separate occasions, they have exceeded the limit of 130 metric tons of heavy water." I looked into it and found the relevant language in paragraph 14 of Annex 1 of the JCPOA [5]. From page 24 of the PDF:

"All excess heavy water which is beyond Iran's needs for the modernised Arak research
reactor, the Zero power heavy water reactor, quantities needed for medical research
and production of deuterate solutions and chemical compounds including, where
appropriate, contingency stocks, will be made available for export to the international
market based on international prices and delivered to the international buyer for 15
years. Iran's needs, consistent with the parameters above, are estimated to be 130
metric tonnes of nuclear grade heavy water or its equivalent in different enrichments"

Refer to IAEA reports [6] dated 26 February 2016 [7], 9 November 2016 [8] for the two occasions that are referenced. Iran's needs of heavy water were estimated to be 130 metric tonnes. Beyond that, they would have to sell and deliver the water to an international buyer. IAEA reports indicate that this is what Iran was doing. Paragraph 10 of the Nuclear section of the JCPOA contains more language relating to heavy water. From page 9 of the PDF:

"There will be no additional heavy water reactors or accumulation of heavy
water in Iran for 15 years. All excess heavy water will be made available for
export to the international market"

Again, it appears that this is in-line with what Iran was doing. Heavy water in excess of 130 metric tonnes was sold and delivered to international buyers. In addition to the 130 metric tonnes stored within Iran, heavy water was allowed by the Joint Commission to be stored outside of Iran, with some sources [9] calling this a loophole in the cap. Regardless of whether or not you believe that exceeding the 130 metric tonnes of heavy water constitutes a violation, there's a dispute resolution mechanism included in the JCPOA. See paragraphs 36-37 on pages 19-20 of the PDF. The US could have used this dispute resolution process to address concerns about violations of the agreement, but did not.

I will take your "path" to refer to the JCPOA. It should be clear that rather than Iran first stepping off this path, it was the US that did so. It was not after all processes set forth in the agreement were exhausted that the US left the agreement, but instead the decision is made in lieu of engaging in dispute resolution. Note that in the withdrawal briefing [4] President Trump made no references to violations of the JCPOA by Iran, but instead lists criticisms of the JCPOA itself. Given that the US did not utilize the dispute resolution mechanism process established by the JCPOA, and the fact that criticisms of the JCPOA greatly outnumber the Iranian violations of the JCPOA, it is my view that the withdrawal from the JCPOA by the US was not in response to Iran straying from the path.

There are a couple of other grievances that President Trump cited in his October 2017 [3] briefing, but I could find no support for them, and so I don't address them here.

[0] https://www.iaea.org/sites/default/files/19/06/gov2019-21.pd...

[1] https://news.yahoo.com/iran-still-holding-end-nuclear-deal-i...

[2] https://www.reuters.com/article/us-iran-nuclear-iaea/iran-st...

[3] https://www.whitehouse.gov/briefings-statements/remarks-pres...

[4] https://www.whitehouse.gov/briefings-statements/remarks-pres...

[5] https://assets.documentcloud.org/documents/2165399/full-text...

[6] https://www.iaea.org/newscenter/focus/iran/iaea-and-iran-iae...

[7] https://www.iaea.org/sites/default/files/gov-2016-8-derestri...

[8] https://www.iaea.org/sites/default/files/16/11/gov2016-55.pd...

[9] https://isis-online.org/uploads/isis-reports/documents/Closi...